Heterostructured CoS2/CuCo2S4@N-doped carbon hollow sphere for potassium-ion batteries

Dynamic Induction of Conversion-Based Anode Degradation by Valence State and Mechanical Cracks

Electrochemical energy storage through conversion reactions in crystalline electrode materials primarily depends on the size of guest ions. In this study, a combination of synchrotron-based transmission X-ray microscopy and X-ray absorption near edge spectroscopy is utilized to reveal the dynamic physicochemical changes in the micro-regions of spherical NiS2 active particles during the potassiation/depotassiation process. The findings show that, as the degree of potassiation increases, visible cracks and voids form within the bulk material, with significant differences in the chemical valence states of metal elements between the inner and outer regions. Furthermore, the voids induce the formation of new cracks, which propagate extensively into the bulk, serving as the root cause of electrode particle failure. Based on these observations, it is also demonstrated that this failure phenomenon in active materials can be mitigated through dimensional engineering strategies, paving the way for the development of high-capacity and highly stable potassium-ion batteries.

Yolk-shell FeS@N-doped carbon nanosphere as superior anode materials for sodium-ion batteries

Iron sulfides have shown great potential as anode materials for sodium-ion batteries (SIBs) because of their high sodium storage capacity and low cost. Nevertheless, iron sulfides generally exhibit unsatisfied electrochemical performance induced by sluggish electron/ion transfer and severe pulverization upon the sodiation/desodiation process. Herein, we constructed a yolk-shell FeS@NC nanosphere with an N-doped carbon shell and FeS particle core via a simple hydrothermal method, followed by in-situ polymerization and vulcanization. The FeS particles intimately coupled with N-doped carbon can accelerate the electron transfer, avoid severe volume expansion, and maintain structural stability upon repeated sodiation/desodiation process. Furthermore, the small particle size of FeS can shorten ion-diffusion distance and facilitate ion transportation. Therefore, the FeS@NC nanosphere shows excellent cycling performance and superior rate capability that it can deliver a high capacity of 520.1 mAh g-1 over 800 cycles at 2.0 A g-1 and a remarkable capacity of 625.9 mAh g-1 at 10.0 A g-1.

Dual engineering of hetero-interfaces and architecture in MoSe2/VSe1.6@NC nanoflower for fast and stable sodium/potassium storage

Rational structure design is significant for the selenide anodes in the sodium/potassium ion batteries (SIBs/PIBs). Herein, dual engineering of hetero-interfaces and architecture is proposed to design SIB/PIB anodes. Attributed to the coordination binding with Mo7O246- and VO3-, the polydopamine assembly is demonstrated as an ideal template to produce bimetallic selenide of MoSe2/VSe1.6 anchoring on the in-situ N-doped carbon matrix (MoSe2/VSe1.6@NC). This ingenious hierarchical nanoflower structure can shorten the Na+/K+ diffusion length, increase the electron conductivity and buffer the volume changes, which can promote Na+/K+ reaction kinetics and stabilize the cycling performance. Consequently, the sodium/ potassium storage performance of MoSe2/VSe1.6@NC can be boosted. In SIBs, it achieves a capacity of 202 mAh/g at 10.0 A/g for 5000 cycles. Meanwhile, stable capacities of 207.1 mAh/g can be reached at 1.0 A/g over 1000 cycles in the PIBs. Furthermore, impressive capacities of 222.1 mAh/g and 100.4 mAh/g are delivered in the full cells of MoSe2/VSe1.6@NC//Na3V2(PO4)3@C and MoSe2/VSe1.6@NC//FePBA, respectively. This proves the potential practical application for the MoSe2/VSe1.6@NC anode in SIBs/PIBs.

Double S-scheme Cu2-xSe/twinned-Cd0.5Zn0.5S homo-heterojunctions with surface plasmon effects for efficient photocatalytic H2 evolution

The enhancement of charge separation and utilization efficiency in both the bulk phase and interface of semiconductor photocatalysts, as well as the expansion of light absorption range, are crucial research topics in the field of photocatalysis. To address this issue, twinned Cd0.5Zn0.5S (T-CZS) homojunctions consisting of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (ZB-CZS) were synthesized via a hydrothermal method to facilitate the bulk-phase charge separation. Meanwhile, Cu2-xSe with localized surface plasmon resonance effect (LSPR) generated by Cu vacancies was also obtained through a hydrothermal process. Due to their opposite electronegativity, a solvent evaporation strategy was employed to combine Cu2-xSe and T-CZS by intermolecular electrostatic. After optimization, the photocatalytic hydrogen (H2) evolution rate of 5 wt% Cu2-xSe/T-CZS reached an impressive value of 60 mmol∙h-1∙g-1, which was 4.6 and 66.6 times higher than that of pure Cu2-xSe and T-CZS, respectively. Furthermore, this composites demonstrated a remarkable rate of 0.46 mmol∙h-1∙g-1 under near-infrared (NIR) wavelength (>800 nm). The enhanced performance observed in Cu2-xSe/T-CZS can be attributed to its unique and efficient double S-scheme charge transfer mechanism which effectively suppresses rapid recombination of electron-hole pairs both within the bulk phase and at the surface interfaces; this conclusion is supported by Density Functional Theory (DFT) calculations as well as electron paramagnetic resonance spectroscopy analysis. Moreover, incorporation of Cu2-xSe enables effective utilization ultraviolet visible-near infrared (UV-Vis-NIR) light by the composites while facilitating injection "hot electrons" into T-CZS for promoting photocatalytic reactions. This study provides a potential strategy for achieving efficient solar energy conversion through synergistic integration of non-stoichiometric plasmonic materials with photocatalysts with twinned-twinned structures.

Ni-Based Catalysts for CO2 Methanation: Exploring the Support Role in Structure-Activity Relationships

The catalytic hydrogenation of CO2 to methane is one of the highly researched areas for the production of chemical fuels. The activity of catalyst is largely affected by support type and metal-support interaction deriving from the special method during catalyst preparation. Hence, we employed a simple solvothermal technique to synthesize Ni-based catalysts with different supports and studied the support role (CeO2, Al2O3, ZrO2, and La2O3) on structure-activity relationships in CO2 methanation. It is found that catalyst morphology can be altered by only changing the support precursors during synthesis, and therefore their catalytic behaviours were significantly affected. The Ni/Al2O3 with a core-shell morphology prepared herein exhibited a higher activity than the catalyst prepared with a common wet impregnation method. To have a comprehensive understanding for structure-activity relationships, advanced characterization (e. g., synchrotron radiation-based XAS and photoionization mass spectrometry) and in-situ diffuse reflectance infrared Fourier transform spectroscopy experiments were conducted. This research opens an avenue to further delve into the role of support on morphologies that can greatly enhance catalytic activity during CO2 methanation.

Cobalt-vanadium sulfide yolk-shell nanocages from surface etching and ion-exchange of ZIF-67 for ultra-high rate-capability sodium ion battery

Development of high-performance metal sulfides anode materials is a great challenge for sodium-ion batteries (SIBs). In this work, a cobalt-based imidazolate framework (ZIF-67) were firstly synthesized and applied as precursor. After the successive surface etching, ion exchange and sulfidation processes, the final cobalt-vanadium sulfide yolk-shell nanocages were obtained (CoS2/VS4@NC) with VS4 shell and CoS2 yolk encapsulated into nitrogen doped carbon frameworks. This yolk-shell nanocage structure effectively increases the specific surface area and provides enough space for inhibiting the volume change during charge/discharge processes. Besides, the nitrogen doped carbon skeleton greatly improves the ionic conductivity and facilitates ion transport. When used as the anode materials for SIBs, the yolk-shell nanocages of CoS2/VS4@NC electrode exhibits excellent rate capability and stable cycle performance. Notably, it displays a long-term cycling stability with excellent capacity of 417.28 mA h g-1 after 700 cycles at a high current density of 5 A/g. This developed approach here provides a new route for the design and synthesis of various yolk-shell nanocages nanomaterials from enormous MOFs with multitudinous compositions and morphologies and can be extended to the application into other secondary batteries and energy storage fields.

Carbon-supported T-Nb2O5 nanospheres and MoS2 composites with a mosaic structure for insertion-conversion anode materials

Reasonably combining the strengths of insertion and conversion anode materials to create an advanced anode material remains a formidable challenge for rechargeable lithium-ion batteries (LIBs). In this work, bulk MoS2 embedded with T-Nb2O5 nanospheres was synthesized via a simple hydrothermal process and a polydopamine carbon source was introduced by heat treatment. The design strategy can effectively accelerate the charge transfer and reduce the volume expansion during electrochemical cycling, leading to an improvement in lithium storage performance. As a consequence, the coexistence of T-Nb2O5, MoS2 and C can achieve the best synergistic effect when the molar ratio of Nb and Mo sources was 1 : 1. Notably, the T-Nb2O5@MoS2@C-1-1 electrode not only delivered an excellent reversible capacity of 518 mA h g-1 at a current density of 0.1 A g-1 but also exhibited superb cycling stability. The specific capacity of this electrode maintained 187 mA h g-1 at 2 A g-1 after 1000 cycles with a negligible capacity fading rate of only 0.015% per cycle.

Bimetallic MnMoO4 nanostructures on carbon fibers as flexible cathode for high performance zinc-ion batteries

Aqueous zinc ion batteries (ZIBs) are promising energy storage devices due to the advantageous features of Zn. However, developing suitable cathode materials with high performance is still an urgent task for the development of ZIBs. In this work, we report on the preparation of a flexible cathode for ZIBs consisting of carbon fiber supported MnMoO₄ nanostructures protected with N-doped carbon coatings (CF/MnMoO4@NCs). The N-doped carbon coating on MnMoO₄ nanostructures can buffer volume expansion of MnMoO₄, and the CF and NCs with good electronic conductivity can facilitate quick electrons transportation in the CF/MnMoO₄@NCs system. The optimized CF/MnMoO₄@NCs cathode exhibits high capacity and good rate capability. Specifically, it delivers an outstanding discharge capacity of 663 mA h g^-1 at a current density of 0.1 A/g after 100 cycles, and at a current density of 2 A/g, the cathode can still achieve a discharge capacity of 212 mA h g^-1. This work expands the choice of cathode material and provides constructive direction on designing high-performance cathode materials for ZIBs.

Tin disulfide embedded on porous carbon spheres for accelerating polysulfide conversion kinetics toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation advanced energy storage systems due to their high theoretical capacity, low cost and environmental friendliness. However, the severe shuttle effect and weak redox reaction severely restrict the practical application of Li-S batteries. Herein, a functional catalytic material of tin disulfide on porous carbon spheres (SnS₂@CS) is designed as a sulfur host and separator modifier for lithium-sulfur batteries. SnS₂@CS with high electrical conductivity, high specific surface area and abundant active sites can not only effectively improve the electrochemical activity but also accelerate the capture/diffusion of polysulfides. Theoretical calculations and in situ Raman also demonstrate that SnS₂@CS can efficiently adsorb and catalyse the rapid conversion of polysulfides. Based on these advantages, the SnS₂@CS-based Li-S battery delivers an excellent reversible capacity of 868 mAh/g at 0.5C (capacity retention of 96 %), a high rate capability of 852 mAh/g at 2C, and a durable cycle life with an ultralow capacity decay rate of 0.029 % per cycle over 1000 cycles at 2C. This work combines the design of sulfur electrodes and the modification of separators, which provides an idea for practical applications of Li-S batteries in the future.

Surface engineered hollow Ni-Co-P@TiO2-x nanopolyhedrons as high performance anode material for sodium storage

With the proposal of carbon peaking and carbon neutrality goals, clean energy storage is attracting more and more attentions. In view of the lack of lithium resource in our earth, sodium-ion batteries are considered as the emerging and promising next-generation energy storage devices. Appropriate high-performance anode materials play a vital role in the development of sodium-ion batteries. Here, a core-shell hollow Ni-Co-P nanopolyhedron interconnected by oxygen defect TiO₂ (Ni-Co-P@TiO_2-x) is reported, which is synthesized by ion etching-hydrolysis and subsequent phosphatization/hydrogenation treatment using ZIF-67 as template and hybrid carbon source. The achieved Ni-Co-P@TiO_2-x material has several distinct advantages including hollow core-shell structure, flexible conductive carbon matrix, stable electroactive coating layer, and efficient pseudocapacitive behavior, resulting in high reversible capacities, remarkable rate capability and excellent cycle stability. The synergetic battery-capacitor characteristic of Ni-Co-P@TiO_2-x material makes it become a promising anode for sodium-ion batteries.

Synergistically Achieving Superior Sodium Storage of Metal Selenides by Constructing N-Doped Carbon Foams and Utilizing Cu-Driven Replacement Reaction

Metal selenides are considered as one of the most promising anode materials for Na-ion batteries owing to high specific capacity and relatively higher electronic conductivity compared with metal sulfides or oxides. However, such anodes still suffer from huge volume change upon repeated Na⁺ insertion/extraction processes and simultaneously undergo severe shuttle effect of polyselenides, thus leading to poor electrochemical performance. Herein, a facile chemical-blowing and selenization strategy to fabricate 3D interconnected hybrids built from metal selenides (MSe, M = Mn, Co, Cr, Fe, In, Ni, Zn) nanoparticles encapsulated in in situ formed N-doped carbon foams (NCFs) is reported. Such hybrids not only provide ultrasmall active nanobuilding blocks (≈15 nm), but also efficiently anchor them inside the conductive NCFs, thus enabling both high-efficiency utilization of active components and high structural stability. On the other hand, Cu-driven replacement reaction is utilized for efficiently inhibiting the shuttle effect of polyselenides in ether-based electrolyte. Benefiting from the combined merits of the unique MSe@NCFs and the utilization of the conversion of metal selenides to copper selenides, the as-obtained hybrids (MnSe as an example) exhibit superior rate capability (386.6 mAh g^-1 up to 8 A g^-1 ) and excellent cycling stability (347.7 mAh g^-1 at 4.0 A g^-1 after 1200 cycles).

Surface-assisted synthesis of biomass carbon-decorated polymer carbon nitride for efficient visible light photocatalytic hydrogen evolution

Template is frequently studied as a structure-directing agent to tune the nanomorphology of photocatalysts. However, the influences of template on the polymerization of precursors and compositions of the resulting samples are rarely considered. Herein, a biomass carbon-modified graphitic carbon nitride (CCNx) with a thin-layer morphology is synthesized via one-pot surface-assisted polymerization of melamine precursor on organic yeast. The formation of the hydrogen bond between melamine and yeast induces a strong interfacial confinement, giving rise to small-sized CCNx. In addition, the carbon materials derived from yeast dramatically broaden n → π* visible light harvesting, improve electron delocalization, and greatly enhance charge carrier separation. The optimized CCNx presents a much higher photocatalytic hydrogen production rate of 2704 μmol g^-1h^-1 under visible light irradiation (λ ≥ 420 nm), which is nearly 11-fold that of its pristine counterpart. This work realizes the synergistic effect between morphology tunning and composition tailoring by using biomass template, which shows a great potential in developing efficient metal-free photocatalysts.

In-situ synthesis of FeS/N, S co-doped carbon composite with electrolyte-electrode synergy for rapid sodium storage

Pyrrhotite (FeS) is extensively investigated as the anode for low-cost sodium-ion batteries (SIBs) due to their natural abundance and high theoretical capacity. However, it suffers from significant volume expansion and poor conductivity. These problems can be alleviated by promoting sodium-ion transport and introducing carbonaceous materials. Here, FeS decorated on N, S co-doped carbon (FeS/NC) is constructed through a facile and scalable strategy, which is the best of both worlds. Moreover, to give full play to the role of the optimized electrode, ether-based and ester-based electrolytes are used for matching. Reassuringly, the FeS/NC composite displays a reversible specific capacity of 387 mAh g^-1 after 1000 cycles at 5A g^-1 in dimethyl ether electrolyte. The even distribution of FeS nanoparticles on the ordered framework of carbon guarantees a fast electron/Na-ion transport channel, and the reaction kinetics can be further accelerated in the dimethyl ether (DME) electrolyte, ensuring the excellent rate capability and cycling performance of FeS/NC electrodes for sodium-ion storage. This finding not only provides a reference for the introduction of carbon via in-situ growth protocol, but also demonstrates the necessity for electrolyte-electrode synergy in realizing efficient sodium-ion storage.

Oxygen vacancy-mediated amorphous GeOx assisted polysulfide redox kinetics for room-temperature sodium-sulfur batteries

The practical applications of room-temperature sodium-sulfur (RT Na-S) batteries have been greatly hindered by the natural sluggish reaction kinetics of sulfur and the shuttle effect of sodium polysulfide (NaPSs). Herein, oxygen vacancy (OV)-mediated amorphous GeOx/nitrogen doped carbon (donated as GeOx/NC) composites were well designed as sulfur hosts for RT Na-S batteries. Experimental and density functional theory studies show that the introduction of oxygen vacancies on GeOx/NC can effectively immobilize polysulfides and accelerate the redox kinetics of polysulfides. Meanwhile, the micro-and mesoporous framework, acting as a reactor for storing active S, is conducive to alleviating the expansion of S during the charging/discharging process. Consequently, the S@GeOx/NC cathode affords a reversible capacity of 1017 mA h g-1 at 0.1 A g-1 after 100 cycles, outstanding rate capability of 333 mA h g-1 at 10.0 A g-1 and long lifespan cyclability of 385 mAh g-1 at 1 A g-1 after 1200 cycles. This work furnishes a new way for the rational design of metal oxides with oxygen vacancies and boosts the application for RT Na-S batteries.

FeP Coated in Nitrogen/Phosphorus Co-doped Carbon Shell Nanorods Arrays as High-Rate Capable Flexible Anode for K-ion Half/Full Batteries

Building a proper flexible electrode with high cycling stability, rate capacity and initial coulombic efficiency (ICE) for flexible potassium-ion batteries (PIBs) remains a challenge. Herein, nitrogen/phosphorus co-doped carbon coated FeP nanorods arrays on carbon cloth (FeP@N, PC NRs/CC) as high-rate capable flexible self-supporting anode was successfully fabricated. The composite electrode combines the advantages of FeP nanorods arrays (FeP NRs), carbon cloth (CC) and N, P co-doped carbon shell (N, P-C), which comprehensively improves the electrochemical stability of the flexible electrode, while the open space between FeP nanorods can facilitate electrolyte impregnation and enhance K⁺ transfer, thus effectively elevating the corresponding rate capability. For the FeP@N, PC NRs/CC electrode, it delivers a reversible capacity of 388.8 mA h g^-1 at 0.5 A g^-1 up to 400 cycles. Even at 1.5 A g^-1, it can still achieve a remarkable rate capacity of 346.9 mA h g^-1. Moreover, the assembled soft-packed cell can always light the LED lights when it is bent at different angles, which exhibits excellent mechanical flexibility.

New enhancement mechanism of an ether-based electrolyte in cobalt sulfide-containing potassium-ion batteries

The performance of potassium (K)-ion batteries (KIBs) is not only dependent on electrode materials but also highly related to the electrolyte. In this work, we obtained a cobalt sulfide (CoS)-containing hybrid by the hydrothermal method and subsequent thermal treatment for K-ion storage. After ether-based electrolyte matching, the CoS-containing hybrid achieves a specific capacity of 229 mA h g^-1 at 1 A g^-1 after 300 cycles, and presents enhanced performance in the ether-based electrolyte. According to our measurement and calculation, the CoS-containing hybrid in the ether-based electrolyte promotes the formation of a highly anionic coordination solvated structure, which contributes to the enhancement of the stability of the electrolyte for K-ion storage. In addition, the strong coordination of anions also facilitates the rapid separation of the solvent during the potassiation process, which is also in favor of the decrease of the side reaction of the CoS@RGO hybrid for KIBs. We believe that our work will provide a new perspective on electrolyte engineering to boost the electrode material performance for K-ion storage.

One-Pot Synthesis of LiFePO4/N-Doped C Composite Cathodes for Li-ion Batteries

LiFePO4/N-doped C composites with core-shell structures were synthesized by a convenient solvothermal method. Cetyltrimethylammonium bromide (CTAB) and glucose were used as nitrogen and carbon sources, respectively. The growth of LiFePO4 nanocrystals was regulated by CTAB, resulting in an average particle size of 143 nm for the LiFePO4/N-doped C. The N atoms existed in the carbon of LiFePO4/N-doped C in the form of pyridinic N and graphitic N. The LiFePO4/N-doped C composites delivered discharge specific capacities of 160.7 mAh·g-1 (0.1 C), 128.4 mAh·g-1 (5 C), and 115.8 mAh·g-1 (10 C). Meanwhile, no capacity attenuation was found after 100 electrochemical cycles at 1 C. N-doping enhanced the capacity performance of the LiFePO4/C cathode, while the core-shell structure enhanced the cycle performance of the cathode. The electrochemical test data showed a synergistic effect between N-doping and core-shell structure on the enhancement of the electrochemical performance of the LiFePO4/C cathode.

Ternary Nanohybrid of Ni3S2/CoMoS4/MnO2 on Nickel Foam for Aqueous and Solid-State High-Performance Supercapacitors

To overcome the issues related to supercapacitor (SC) electrodes, such as high cost, low specific capacitance (C_s), low energy density (ED), requirements for expensive binder, etc., binderless electrodes are highly desirable. Here, a new ternary nanohybrid is presented as a binder-free SC electrode based on Ni₃S₂, CoMoS₄, and MnO₂. A facile two-step hydrothermal route, followed by a short thermal annealing process, is developed to grow amorphous polyhedral structured CoMoS₄ and further wrap MnO₂ nanowires on Ni foam. This rationally designed binder-free electrode exhibited the highest C_s of 2021 F g⁻¹ (specific capacity of 883.8 C g⁻¹ or 245.5 mAh g⁻¹) at a current density of 1 A g⁻¹ in 1 M KOH electrolyte with a highly porous surface morphology. This electrode material exhibited excellent cycling stability (90% capacitance retention after 4000 cycles) due to the synergistic contribution of individual components and advanced surface properties. Furthermore, an aqueous binder-free asymmetric SC based on this ternary composite exhibited an ED of 20.7 Wh kg⁻¹, whereas a solid-state asymmetric SC achieved an ED of 13.8 Wh kg⁻¹. This nanohybrid can be considered a promising binder-free electrode for both aqueous and solid-state asymmetric SCs with these remarkable electrochemical properties.

Polyvinylpyrrolidone-regulated synthesis of hollow manganese vanadium oxide microspheres as a high-performance anode for lithium-ion batteries

We report the fabrication of well-defined phase-pure Mn₂V₂O₇ hollow microspheres (h-MVO), assembled from the porous plate-like building blocks, via a facile solvothermal method followed by annealing, with the assistance of polyvinylpyrrolidone (PVP) as the structure-regulating agent. The microstructure dependent electrochemical properties of h-MVO as anode materials for lithium ion batteries (LIBs) are investigated, and excellent lithium storage performance is obtained with a reversible capacity of 1707 mAh g^-1 after 700 cycles at 0.5 A g^-1, revealing that the unique hierarchical framework of the h-MVO microspheres with hollow interiors and porous building blocks could not only accelerate the transport of Li⁺ ions and electrolyte, but also efficiently suppress the electrode pulverization upon cycling. More importantly, we demonstrate that PVP can be an effective agent to tune the microstructures, which would be promising for the development of high-performance energy storage devices.

Implantation of Fe7S8 nanocrystals into hollow carbon nanospheres for efficient potassium storage

As a desirable candidate for lithium-ion batteries, potassium-ion batteries (PIBs) have aroused great interest because of their low cost and high power and energy densities. However, the insertion/extraction of K⁺ with a large radius (1.38 Å) usually bring about the destruction of the electrode materials. Here, ultrafine Fe₇S₈ nanocrystals are successfully implanted into hollow carbon nanospheres (Fe₇S₈@HCSs) via a facile solvothermal method and subsequent novel low-temperature sulfurization, which avoid the aggregation of Fe₇S₈ nanoparticles produced during high-temperature sulfidation. The ultrafine Fe₇S₈ nanoparticles and hollow carbon spheres can not only buffer the severe expansion/shrinkage of electrode materials caused by the repeated insertion/extraction of K⁺, but also provide additional accessible pathways for the high-rate K⁺ transmission. When tested as an anode material for PIBs, Fe₇S₈@HCSs achieve impressive K⁺ storage capacity of 523.2 mAh g^-1 at 0.1 A g^-1 after 100 cycles and remarkable rate capacity of 176.3 mAh g^-1 at 5 A g^-1. Further, assembling this anode with a K₂NiFe(CN)₆ cathode yields stable cycling performance, revealing its great potential for large-scale energy storage applications.